Borehole tools are sometimes pressure operated using pressure built up on an object, usually a sphere, which is pumped or dropped to a seat in a desired location. Upon contact with the seat, the pressure can build on the seated ball to activate one or more tools. Frequently, the activated tool is a packer. Other tools that can be reconfigured with pressure on a landed object on a seat can be sliding sleeves, anchors, centralizers, crossovers or bridge plugs to name a few examples. The boreholes where such seats are located are not always in a vertical configuration, so more often than not the ball is pumped until landed on the seat. At that point, the surface pressure jumps as a signal to the rig crew that the ball has landed on the seat.
In some operations, there is a need to keep the ball seated even after a tool was set with pressure on the ball. For example, if acid or a lost circulation material is pumped after the tool is activated with pressure on a seated ball and the ball does not remain seated against the seat, the acid or lost circulation material will go around the ball and further into the hole where equipment can be damaged or destroyed. In a horizontal run, this is particularly problematic because gravity will not aid in keeping the ball on the seat. Some of the treatment materials that need to be stopped by the seated ball are highly viscous formation sealing materials, making ball retaining mechanisms with moving parts problematic as the movement can be precluded by the coating up of the moving parts from the treatment fluid.
Several designs have been offered for retention of generally metallic balls to their respective seat with some axial play or limited axial play. These designs have generally featured movable components subject to getting gummed up by viscous fluids. Others push the ball through an interference fit in the hope it will not only reach its target and seat but then it will stay in position near the seat. This design is shown in US 2013/0222148 FIG. 7 at 408. US 2014/0318816 shows the use of a snap ring or split ring such as 98 in FIG. 3 to retain the ball B close to the seat 100 with an enlarged view shown in FIG. 4. In these figures, the ball can still move axially away from its seat but in FIG. 12 the snap ring 216 is located in close proximity of the ball B so that after the ball spreads ring 216 to get past it, the ring 216 snaps closed with the hope that the ball stays against the seat.
Combining the need to keep a ball against a seat and an application where there is a viscous material that prevents the reliable use of intricate moving parts presents unique design challenges. However, since applications using such materials also involve the use of non-metallic balls, a workable solution has been developed to address the problem of reliably retaining the ball to the seat which forms a part of the present invention. The seat assembly is provided with at least one downhole oriented barb akin to an upside down hook mounted in the wall uphole of the ball seat. As the ball passes, it is forced past the barb, placing an axial notch in the ball that continues to get longer until the ball finds its seat. At that time the bottom of the barb defines the lower end of the axial groove formed in the ball from forcing it past the barb. Any tendency of the ball to move away from the seat brings the bottom of the groove made in the ball against the barb and all motion stops. These and other aspect of the present invention will be more readily apparent to those skilled in the art form a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.